In high temperature superconductors, the layers contain planar structural units which contain tightly bonded CuO.sub.2 planes. These planes also determine substantially the lattice constants a and b within the layer planes (for high temperature superconductors a.apprxeq.b.apprxeq.3.9 Angstroms). The layer structure ensures, for example, a high critical current density and a relatively large coherence length in the layer planes as well as a small critical current perpendicular to the layer planes along the crystallographic c-axis.
In order to produce, for example, components with planar high temperature superconductor (HTSC) Josephson contacts it has been desirable to produce very many simple layer sequences as required and to provide an access to the film surfaces of the well-conducting a, b planes of the Josephson contact electrodes (or to the later internal boundary surfaces of the Josephson contacts).
Furthermore it is important to prepare the epitaxial thin films as unidirectionally oriented domains which avoid grain boundaries. Grain boundaries between differently oriented domains give rise to undesirably weakened superconductive regions which disrupt the function of the component.
The epitaxial HTSC thin films are as a rule grown on (preferably perovskite-like) substrates with cubic or pseudocubic (slightly distorted from the cubic) crystal structures with the greatest possible matching of the lattice constants (a.sub.substrate .apprxeq.a.sub.film .apprxeq.b.sub.film).
Typically the lattice defect match ##EQU1## is less than several percent.
On (001) oriented substrates, up to now, epitaxial HTSC thin films have been deposited with layer planes perpendicular to normals to the substrate surface as is shown in FIG. 1a and which are described as c-axis oriented films, the deposition being effected at relatively high substrate temperatures which has its basis in the fact that, as a rule, only such films have the characteristics necessary for applications which require a relatively high current carrying capacity.
An orientation with the conducting planes perpendicular to the surface can be achieved only for relatively low substrate temperatures. These so-called a-axis oriented films are comprised of domains with opposite c-axes oriented perpendicularly to one another in the thin film plane. Both the low substrate temperature and the resulting grain boundaries between the domains give rise to a diminution of the superconductive characteristics of these films as is known for example from Journal of Appl. Phys., 70, (1991), 7167 or Physica C 194, (1992), 430.
Phys. Rev. B. 46, (1992), 11902 or Proceedings of European Conf. on Appl. Superconductivity (EUCAS '93), Oct. 4-8, 1993 , Gottingen, describe the growth of thin films for (101)-oriented substrates at high substrate temperatures with (103)-oriented or (103)-oriented domains, whose CuO.sub.2 planes are tilted by 45.degree. to the substrate surface. These so-called (103)-films have a very complicated microstructure with different types of 90.degree. different grain boundaries between the two domains of orientation. In this case, the crystal growth front does not run, during the thin film deposition, parallel to the (103)-plane, i.e. the film surface is very rough and gives rise to the fact that only a small part of the conductive CuO.sub.2 layer planes reach the film surface.
Furthermore, from Appl. Phys. Lett., 61, (1992), 607 it is known to produce (105)-oriented YBa.sub.2 Cu.sub.3 O.sub.7 films on (305) substrates in which the CuO.sub.2 planes are tilted by an angle of 31.degree. relative to the substrate surface. The critical current density in the film plane along the (501) direction is only about 10.sup.3 A/cm.sup.2 at 77K and thus is less usable. Furthermore with relatively small tilting angles of the planes, the number of CuO.sub.2 planes per unit area of the surface is markedly reduced.